While the growth of neuronal population has been well-characterized in vivo, underlying molecular mechanisms remains undefined. The goal of this proposal is to define the role of PACAP (pituitary adenylate cyclase activating peptide) in regulating the three principal mechanisms contributing to neuronal population growth including 1) stimulating mitosis of precursor or neuroblasts, 2) enhancing survival of proliferating precursors and 3) promoting longer-term survival through action of target-derived neurotrophic factor s. PACAP may be critical to normal brain development, since this neuropeptide influences neurogenic and survival of multiple prenatal and postnatal as well as peripheral and central populations. Our specific aim are to define the effects of PACAP on neuroblast mitosis and survival as well as expression of the trk family mRNA's. Second, characterized the effect of PACAP on second messenger systems: cAMP and phosphatidyl inositol (PI) metabolism. Third, define dht regulation and expression of PACAP protein and mRNA in the neurogenetic populations, and characterized peptide autocrine and autoregulatory activity. Fourth, characterized PACAP induction of DNA binding activities that interact with cAMP response elements (CRE's) and other DNA sites in target neuronal gene promoter. Our strategy employs pure populations of mitotic neuroblasts from embryonic sympathetic and sensory ganglia, cerebral cortical neuroepithelium and postnatal cerebellar cortex to identity population- specific and age-dependent PACAP regulation. We examine mitogenic and trophic effects by assaying cell number, [3H]thymidine incorporation, and neurite outgrowth. cAMP and PACAP protein will be assessed y radioimmunoassay an PI metabolism by ion-exchange chromatography. mRNA;s will be assayed by Norther analysis. PACAP induction of population- specific binding activities will be characterized by gel retardation, DNAse I footprinting, and UV crosslinking procedures. By characterizing PACAP actions in peripheral and central neurogenetic populations, we many define mechanisms by which the single peptide, PACAP, differentially regulates population-specific neurogenesis and survival. Hopefully we may learn how extracellular signals, acting via second messenger and transcriptional pathways, alter neuroblast division, survival and trophic factor receptor expression to generate diverse neuronal populations. Insight into second messenger and transcription pathways underlying PACAP mitogenic and trophic activity may identify loci where disease processes intervene to produce dysraphic sates, holoprosencephaly, and systems disorders.